Poly-ethynyl-substituted aromatic compounds in which a π (pi) electron system is bonded to the benzene ring with a triple bond have been considered to be applied as liquid crystals, nonlinear optical materials and electroconductive materials, and are a group of compounds useful as synthetic blocks for dendrimer type π conjugated systems and carbon-rich materials of optical and photochemical interests.
Although these compounds have been usually prepared by a catalytic coupling reaction of a halogenated benzene with acetylene (generally referred to as the Sonogashira reaction) [R. Diercks, J. C. Armstrong, R. Boese, K. P. C. Vollhardt, Angew. Chem., Int. Ed. Engl., 25, 268(1986)], the efficiency of the coupling reaction is not high except for the compounds having phenyl group at its acetylene terminal. For instance, hexakis[(trimethylsilyl)ethynyl]benzene is prepared by coupling of hexabromobenzene with (trimethylsilyl)acetylene, but its yield is at most 30%. Also, there has hitherto been no general and efficient process for preparing a poly-ethynyl-substituted aromatic compound having a different substituent at its acetylene terminal at all, nevertheless there are of increasing interests from the viewpoints of the above applications [conventional processes: J. E. Anthony, S. I. Khan, Y. Rubin, Tetrahedron Lett., 38, 3499 (1997); Y. Tobe, K. Kubota, K. Naemura, J. Org. Chem., 62, 3430 (1997); J. D. Tovar, N. Jux, T. Jarrosson, S. I. Khan, Y. Rubin, ibid, 62, 3432 (1997)].
In addition, in the conventional processes for preparing poly-ethynyl-substituted aromatic compounds, substitution patterns for poly-ethynyl-substituted aromatic compounds having different ethynyl-terminal substituents could not have been controlled.